As is well known in the industry, the manufacturing process of various kinds of electronic or semiconductor devices such as ICs, LSIs and the like involves a fine patterning of a resist layer on the surface of a substrate material such as a semiconductor silicon wafer. This fine patterning process has traditionally been conducted by the photolithographic method in which the substrate surface is uniformly coated with a positive or negative tone photoresist composition to form a thin layer of the photoresist composition and selectively irradiating with actinic rays (such as ultraviolet light) through a photomask followed by a development treatment to selectively dissolve away the photoresist layer in the areas exposed or unexposed, respectively, to the actinic rays leaving a patterned resist layer on the substrate surface. The thus obtained patterned resist layer is utilized as a mask in the subsequent treatment on the substrate surface such as etching, plating, chemical vapor deposition and the like. The fabrication of structures with dimensions of the order of nanometers is an area of considerable interest since it enables the realization of electronic and optical devices which exploit novel phenomena such as quantum confinement effects and allows greater component packing density. Thus, the resist layer is required to have an ever-increasing fineness. One method which can be used to accomplish this is by using actinic rays having a shorter wavelength than the conventional ultraviolet light, such as, for example, electron beams (e-beams), excimer laser beams, EUV, BEUV and X-rays, used as the short wavelength actinic rays. Needless to say, the minimum size obtainable is primarily determined by the performance of the resist material and the wavelength of the actinic rays. Various materials have been proposed as suitable resist materials.
Many positive photoresists they generally apply a technique called “chemical amplification” to the polymeric resist materials. A chemically amplified resist material is generally a multi-component formulation in which there is a main polymeric component, such as a novolac resin which contributes towards properties such as resistance of the material to etching, mechanical stability and developability; and one or more additional components which impart desired properties to the resist and a photoacid generator. Typically, a portion of the hydroxy groups of a phenolic polymer, such as a novolac, a polyhydroxystyrene and the like, is protected by a functional group which reacts with an acid and is removed to de-protect the hydroxy group making the hydroxy group available for other reactions, which in positive photoresists is developability. By definition, the chemical amplification occurs through a catalytic process involving the sensitizer which results in a single irradiation event causing a cascading effect by reacting with multiple functional groups of the protected novolac molecules. In a typical example the resist comprises a polymer and a photoacid generator (PAG) as sensitizer. The PAG releases a proton in the presence of actinic radiation (light or e-beam). This proton then reacts with the polymer to cause it to lose the functional group thus deprotecting the hydroxy group. In the process, a second proton is generated which can then react with a further molecule.
Many negative photoresists rely on photogenerated acid to cause either crosslinking or polymerization of the resist components so that the exposed areas are insoluble to developers, either solvent or aqueous based, particularly aqueous base developers. The process for these resists generally require a heating step to efficiently and effectively cause the reactions, polymerization or crosslinking, to occur since at room temperature there is not enough polymerization or crosslinking to make the resist impervious to the developer. Most of these negative working resists also require a post bake to further cure the remaining resist patterns.
Negative photoresists have also been described which combine chemically amplified positive resist chemistry with negative working curing agents, such as crosslinkers. In these photoresists, a phenolic polymer, whose hydroxy groups are partially protected, is combined with a crosslinker and a photoacid generator. During exposure, the protected hydroxy groups are de-protected and free to react with the crosslinking groups, see for example, U.S. Pat. No. 6,114,082 to Hakey. In this disclosure, the phenolic polymer is required to be partially protected (75% protection) so that, after exposure, an aqueous base developer can solubilize the unexposed areas thus allowing a negative image to remain. Also disclosure is the requirement that post exposure heating be performed to properly cure the resist to prevent the developer from attacking the exposed areas of the resist. The speed of the curing reaction can be controlled, for example, by heating the resist film after exposure (post exposure bake or PEB) to drive the reaction that causes the loss of the functional group and/or the crosslinking/curing. Also during heating, the reacted polymer molecules are free to react with remaining components of the formulation, as would be suitable for a negative-tone resist. As mentioned these systems require heating of the resist to complete the required crosslinking so that the exposed areas are insoluble to the developer.
A well-known and documented issue with chemically amplified resists is a phenomenon knowns as “resist blur” or “dark reaction”. In the process the photogenerated acid migrates away from the exposed areas (acid migration) and into the unexposed areas where it can cause unwanted reactions. In positive resists, line sharpening results and in negative resists line-broadening results. Various methods and resist components have been introduced to control acid diffusion such as the addition of base quenchers which react with diffused acid to remove it from the system prior to any unwanted resist reactions. Addition of base quencher itself bring limitation such as reduced sensitivity, developer issues, etc. Additionally, since most resists require PEB the increased temperature impart higher kinetic energy to the system and thus the acid resulting in increased levels of migration and thus line broadening. In some cases, where small critical dimensions (CD) are required, the exposure latitude of these systems is severely reduced including line bridging and poor resolution.
As can be seen there is an ongoing desire to obtain finer and finer resolution of photoresists that will allow for the manufacture of smaller and smaller semiconductor devices in order to meet the requirements of current and further needs. In order to achieve these lofty goals line broadening and line edge roughness need to be reduced, as well as exposure latitude and contrast need to be improved. It is thus desirable to create materials, compositions and methods which can be used in conjunction with these photoresist processes to create these improvements.